1. Field of the Invention
The present invention relates to a retracting device for a safety syringe, and more particularly to a retracting device which is able to satisfactorily pull the needle hub back into the barrel so that the syringe is able to be safely disposed.
2. Description of Related Art
A conventional syringe is shown in FIG. 6, and has a barrel (5), a needle hub (6) and a plunger (7).
The barrel (5) has a step (51) formed on an inner face thereof. The needle hub (6) has a flange (61) corresponding to the step (51) and having a diameter slightly larger than a diameter of the step (51). The plunger (7) has a stopper (71) and a hook (72) formed on a distal end of the plunger (7). The needle hub (6) further defines an annular cutout (62) to receive therein an engaging portion (711) of the stopper (71) and a retaining portion (63) formed to maintain the stopper (71) to be in engagement with the needle hub (6). The stopper (71) has an extension (712) extending out of the annular cutout (62) to correspond to the hook (72).
When the needle hub (6) is received in the barrel (5), because the diameter of the flange (61) is larger than the step (51), the diameter of the step (51) is enlarged so that the engagement between the needle hub (6) and the barrel (5) is secured. Then, the engaging portion (711) of the stopper (71) is received in the annular cutout (62) of the needle hub (6).
When the plunger (7) is pushed in the barrel (5) toward the needle hub (6), the hook (72) first passes over the extension (712) of the stopper (71) so as to complete an injection. Thereafter, when the user is pulling the needle hub (6) together with the needle (not shown) back into the barrel (5) in order to safely dispose of the syringe, the hook (72) engages with the extension (712) of the stopper (71) and then the user is able to pull the needle hub (6) together with the stopper (71) inward to the inside of the barrel (5).
However, problems often happen to the users when trying to dispose of the syringe of this type. That is, if the engagement between the flange (61) and the step (51) is too tight, the user will have difficulty pulling the needle hub (6) back into the barrel (5) and if the engagement between the flange (61) and the step (51) is too loose, the needle hub (6) will automatically fall into the barrel (5) when the user is trying to have medicine received inside the syringe. Accordingly, a precise calculation of the dimension of the needle hub (6), the plunger (7) and even the barrel (5) should be taken carefully so that a proper engagement among the needle hub (6), the plunger (7) and the barrel (5) is available.
To overcome the shortcomings, the present invention tends to provide an improved retracting device for a safety syringe to mitigate and obviate the aforementioned problems.